A sensitive Ag+-mediated magnetic relaxation and colorimetry dual-mode sensing platform.

To address the relatively low sensitivity of current redox reagent-mediated magnetic relaxation sensing methods, we present a novel Ag+-mediated magnetic sensing platform that enhances the sensitivity by three orders of magnitude. The new sensing platform is based on Ag+-catalyzed oxidation of Mn2+ to KMnO4, accompanied by a distinct color change, which facilitates colorimetric detection. In the case of insufficient Ag+ ions, MnO2 is an additional oxidation product and the KMnO4/MnO2 ratio is dependent on the concentration of Ag+. When combined with a specific quantity of reducing agent, both KMnO4 and MnO2 are reduced to Mn2+ with a large relaxivity, and the concentration of Mn2+ in the resultant solution inversely correlates with the amount of KMnO4 since KMnO4 consumes more reductant during reduction. Consequently, the transverse relaxation rate of the solution exhibits a negative correlation with the Ag+ concentration. Thus, by coupling this Ag+-mediated Mn2+ to KMnO4 transformation with reactions that modulate Ag+ concentration, a dual-mode sensing platform for magnetic relaxation and colorimetry can be realized. Herein, we take H2O2 as an example to verify the detection performance of this sensing platform since H2O2 can oxidize Ag0 in Ag@Fe3O4 nanoparticles to Ag+. Experimental findings demonstrate detection limits of 10 nM and 20 nM for the magnetic relaxation and colorimetry modes, respectively, affirming the excellent sensitivity and the potential practical application of this strategy.

Synthesis and Reactivity of the [NCCCO]- Cyanoketenate Anion.

Cyanoketene is a fundamental molecule that is actively being searched for in the interstellar medium. Its deprotonated form (cyanoketenate) is a heterocumulene that is isoelectronic to carbon suboxide whose structure has been the subject of debate. However, the investigation of cyanoketene and its derivatives is hampered by the lack of practical synthetic routes to these compounds. We report the first synthesis of the cyanoketenate anion in [K(18-crown-6)][NCCCO] (1) as a stable molecule on a multigram scale in excellent yields (>90 %). The structure of this molecule is probed crystallographically and computationally. We also explore the protonation of 1, and its reaction with triphenylsilylchloride and carbon dioxide. In all cases, anionic dimers are formed. The cyanoketene could be synthesized and crystallographically characterized when stabilized by a N-heterocyclic carbene. The cyanoketenate is a very useful unsaturated building block containing N, C and O atoms that can now be explored with relative ease and will undoubtedly unlock more interesting reactivity.

A facile and sensitive magnetic relaxation sensing strategy based on the conversion of Fe3+ ions to Prussian blue precipitates for the detection of alkaline phosphatase and ascorbic acid oxidase.

Herein, a novel magnetic relaxation sensing strategy based on the change in Fe3+ content has been proposed by utilizing the conversion of Fe3+ ions to Prussian blue (PB) precipitates. Compared with the common detection approach based on the valence state change of Fe3+ ions, our strategy can cause a larger change in the relaxation time of water protons and higher detection sensitivity since PB precipitate can induce a larger change in the Fe3+ ion concentration and has a weaker effect on the relaxation process of water protons relative to Fe2+ ions. Then, we employ alkaline phosphatase (ALP) as a model target to verify the feasibility and detection performance of the as-proposed strategy. Actually, ascorbic acid (AA) generated from the ALP-catalyzed L-ascorbyl-2-phosphate hydrolysis reaction can reduce potassium ferricyanide into potassium ferrocyanide, and potassium ferrocyanide reacts with Fe3+ to form PB precipitates, leading to a higher relaxation time. Under optimum conditions, the method for ALP detection has a wide linear range from 5 to 230 mU/mL, and the detection limit is 0.28 mU/mL, sufficiently demonstrating the feasibility and satisfactory analysis performance of this strategy, which opens up a new path for the construction of magnetic relaxation sensors. Furthermore, this strategy has also been successfully applied to ascorbic acid oxidase detection, suggesting its expansibility in magnetic relaxation detection.

Metal-free alkylation of quinoxalinones with aryl alkyl ketones.

The first metal-free method for alkylation of quinoxalinones using cheap and stable aryl alkyl ketones as nucleophilic alkylation reagents is reported. This strategy greatly broadens the application channels of aryl alkyl ketones through carbon-carbon bond activation. In addition, the protocol has the advantages of simple operation, broad substrate scope, and good functional group tolerance.

Copper-promoted difunctionalization of unactivated alkenes with silanes.

An efficient copper-catalyzed cascade difunctionalization of N-allyl anilines toward the synthesis of silylated indolines using commercially available silanes has been reported. This strategy provides a new avenue for the synthesis of a diverse array of indolines in reasonable yields. Preliminary mechanistic investigations indicate that the reaction probably proceeds via a radical pathway with unactivated alkenes as radical acceptors and simple silanes as radical precursors. This protocol is distinguished by its atom economy, broad substrate scope and readily available starting materials.

Fe-Ti bimetal oxide adsorbent for removing low concentration H2S at room temperature.

ABSTRACTHerein, a series of Fe-Ti bimetal oxide adsorbents were prepared by reduction-co-precipitation method, and their performance in removing low concentration H2S at room temperature was investigated. The adsorbents were characterized by X-Ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), Ultraviolet Visible diffuse reflectance spectroscopy (UV-Vis-DRS), X-Ray photoelectron spectroscopy (XPS) and N2 adsorption-desorption. The results showed that the addition of Ti increased the specific surface area, pore volume and small oligomeric Fe2O3 of ferrihydrite. When the Fe/Ti molar ratio was 8:1, Fe-Ti bimetal oxide formed a large amount of oligomeric Fe2O3, and its specific surface area and pore volume reached 344.99 m2/g and 0.34 cm3/g, respectively. At this time, Fe-Ti bimetal oxide exhibited the highest breakthrough sulfur capacity of 222.8 mg/g. High temperature calcination caused Fe-Ti bimetal oxide to form small specific surface area and pore volume, and produced crystalline α-Fe2O3. And the breakthrough sulfur capacity of Fe-Ti bimetal oxide decreased with the increasing calcination temperature. In addition, the desulfurization process conformed to the unreacted shrinking nucleus model.

A Fluorescent Sensor Based on Reversible Addition-Fragmentation Chain Transfer Polymerization for the Early Diagnosis of Non-small Cell Lung Cancer.

We propose a novel, ultrasensitive and low-cost sensor using reversible addition-fragmentation chain transfer (RAFT) polymerization as a signal amplification strategy for the detection of CYFRA 21-1 DNA fragment, a tumor marker of non-small cell lung carcinoma. The peptide nucleic acid (PNA) probes were firstly immobilized on magnetic beads (MBs) to capture the CYFRA 21-1 DNA specifically. After hybridization, CPAD was tethered to the hetero duplexes through carboxylate-Zr4+-phosphate chemistry. Subsequently, a number of fluorescent tags were introduced to the heteroduplexes through RAFT polymerization, leading to an amplification of the fluorescence signal. The sensor demonstrates a low limit of detection (LOD) of 0.02 fM. It has great selectivity with respect to base mismatch DNA, and high anti-interference ability in normal human serum. Overall findings of the study suggest that proposed sensor holds enormous potential to be used as a tool for the early-stage diagnosis of lung cancers.

An ultrasensitive fluorescent aptasensor based on truncated aptamer and AGET ATRP for the detection of bisphenol A.

Given the gigantic harmfulness of bisphenol A (BPA), a novel and ultrasensitive aptasensor, which employs the truncated BPA aptamer, click chemistry, and activators generated by electron transfer for atom transfer radical polymerization (AGET ATRP), was developed herein for the quantitative determination of BPA. Firstly, hairpin DNAs (hairpins) with a thiol at the 5' end and an azide group at the 3' end were conjugated with aminated magnetic beads (MBs) through heterobifunctional cross-linkers. BPA truncated aptamer (ssDNA-A) hybridizes with its complementary single-stranded DNA (ssDNA-B) to form double-stranded DNA. In the presence of BPA, ssDNA-A specifically captures BPA, and then ssDNA-B is released. Subsequently, the ssDNA-B hybridizes with hairpins to expose the azide group near the surface of the MBs. Then, propargyl-2-bromoisobutyrate (PBIB), the initiator of AGET ATRP containing alkynyl group, was conjugated with azide group of hairpins via the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC). Consequently, a large number of fluorescein-o-acrylate (FA) were introduced to the MBs through AGET ATRP, resulting in that the fluorescence intensity was increased dramatically. Obviously, the fluorescence intensity was especially sensitive to the change of BPA concentration, and this method can be used in quantitative determination of BPA. Under optimal conditions, a broad liner range from 100 fM to 100 nM and a low limit of detection (LOD) of 6.6 fM were obtained. Moreover, the method exhibits not only excellent specificity for BPA detection over BPA analogues but high anti-interference ability in real water sample detection, indicating that it has huge application prospect in food safety and environment monitoring.

An electrochemical aptasensor based on eATRP amplification for the detection of bisphenol A.

Herein, a novel aptasensor was constructed for ultrasensitive detection of bisphenol A (BPA). In this method, an electrochemically mediated atom transfer radical polymerization (eATRP) signal amplification strategy was applied to BPA detection for the first time. The 5'-end modified sulfhydryl group and the 3'-end modified azide group hairpin DNA were immobilized on a gold electrode through an Au-S bond. The double-stranded DNA was formed by the hybridization of an aptamer and a single-stranded DNA partially paired with the hairpin DNA. In the presence of BPA, the aptamer combined with BPA and the single-stranded DNA was released to open the hairpin structure, making the azide groups at the 3' end exposed. Subsequently the initiator of eATRP was introduced into hairpin DNA through click chemistry reaction and eATRP was conducted for the polymerization of the electroactive probe ferrocene methyl methacrylate (FMMA). As a result, the ultrasensitive detection of BPA was realized, and the detection limit of this aptasensor was as low as 59 aM and a good selectivity was obtained in the presence of 100-fold structural analogs. The application of this aptasensor was evaluated by detecting BPA in pure water samples, and recoveries were in the range of 95.23-98.40%, holding promising applications in biological analysis.

Hairpin probes based click polymerization for label-free electrochemical detection of human T-lymphotropic virus types II.

A novel, simple, and label-free amplification electrochemical impedance method for quantitative detection of Human T-lymphotropic virus types II(HTLV-II) via click chemistry-mediated of hairpin DNA probes (hairpins) with polymers was developed. The hairpins were firstly attached to the gold electrode surface by an S-Au bond, the azido terminals of hairpins were close to the electrode surface, which make it difficult to be approached. After hybridizing with HTLV-II, the hairpins were unfolded and experienced a big configuration change, which made the azido terminals of the hairpins available to conjugate with alkynyl-containing polymer, called P(DEB-DSDA), formed by 1,4-diacetylenebenzene (DEB) and 4,4'-Diazido-2,2'-stilbenedisulfonic acid disodium salt tetrahydrate (DSDA) via Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC). With amount of P(DEB-DSDA) conjugated with the hairpin probes via click polymerization, its electrochemical signal can have a great amplification. Under optimized experimental conditions, this new probe showed a low detection limit of 0.171 pM with a good liner in the range of 1 pM-1 nM. Meanwhile, the biosensor also exhibited good selectivity and reliability in detection of real serum samples, indicating that it has great application potential in clinical DNA diagnosis and detection.